1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device and method for manufacturing the same, capable of improving an aperture ratio and simplifying the manufacturing process.
2. Description of the Related Art
Liquid crystal display (LCD) devices have advantageous characteristics such as low voltage operation, low power consumption, a lightweight and slim profile, and full color. Accordingly, LCD devices are widely used for display windows of watches, in calculators, as computer monitors, monitors having television receiving functions, television sets, and hand-held terminals.
Currently, TN (Twisted Nematic) mode LCD devices, which are widely used, have narrow viewing angles. Accordingly, technologies for widening such a viewing angles are being studied. As an example of widening the viewing angle, there exist an In Plane Switching (IPS) mode LCD device and a Vertical Alignment (VA) mode LCD device.
IPS mode LCD device widens the viewing angle by forming a pixel electrode and a common electrode together, on a thin film transistor (TFT) substrate. The liquid crystal is operated by a lateral electric field in a horizontal direction. However, IPS mode LCD devices have a problem in that their aperture ratio is lowered due to their structural characteristics.
VA mode LCD devices use a negative-type liquid crystal having a negative (−) dielectric anisotropy. In such devices, when a voltage is not applied, a longer axis direction of a liquid crystal molecule is arranged perpendicularly with respect to a plane of an alignment layer, and when the voltage is applied, the liquid crystal molecule is arranged in parallel on the plane of the alignment layer. An image is displayed by adjusting light transmittance using this property.
VA mode LCD devices distorts the electric field applied to the liquid crystal layer by forming, on the substrate, an auxiliary electrode, an electric field guide window, and a dielectric rib, and aligns a director of the liquid crystal molecule using the distorted electric field, thereby widening the viewing angle.
FIG. 1 is a plan view of a unit pixel of a VA mode LCD device according to the related art, and FIG. 2 is a cross-sectional view taken along line I-I′ of FIG. 1. Referring to FIGS. 1 and 2, the VA mode LCD device includes: first and second substrates 1 and 2; a gate line 7 and a data line 9 respectively formed in horizontal and vertical directions on the first substrate 1 to define a pixel region; a pixel electrode 13 divided into a plurality of electrodes by an electric field guide window 14 formed on the pixel region; an auxiliary electrode 11 formed on the same layer as the gate line 7; a gate insulating layer 3 formed on the first substrate 1 including the gate line 7; a passivation layer 5 formed on the gate insulating layer 3 including the data line 9; a black matrix layer 4 formed on the second substrate 2; a color filter layer 6 formed on the second substrate 2 including the black matrix 4; a common electrode 8 formed on the color filter layer 6; a dielectric rib 10 formed on the common electrode 8; a liquid crystal layer 20 interposed between the first and the second substrates 1 and 2; a first alignment layer 15 formed on the passivation layer 5 including the pixel electrode 13; and a second alignment layer 12 formed on the common electrode 8.
The first and the second alignment layers 15 and 12 may be alignment-processed using a polyamide or polyimide-based compound, Polyvinylalcohol (PVA), polyamic acid and the like. Here, on any of the first and the second alignment layers 15 and 12, a multi-domain that is alignment-processed in a plurality of directions, may be formed. The LCD device that is alignment-processed in the multi-domain in this manner is called a multi-domain vertical alignment (MVA) mode LCD device. The VA mode LCD device that will be described below denotes a MVA mode LCD device.
In the VA mode LCD device according to the related art, when an electric field is generated between the pixel electrode 13 formed on the first substrate 1 and the common electrode 8 formed on the second substrate 2, a fringe field is formed by the electric field guide window 14 and the dielectric rib 10 so that the liquid crystals are aligned differently depending on the fringe field, whereby the viewing angle is compensated in the sense that the alignment angle or the direction of the liquid crystal molecules can be controlled by using the voltage applied to the auxiliary electrode 11 formed on the first substrate 1.
In the related art VA mode LCD device, to align liquid crystal molecules at a desired direction by the fringe field, an interval has to be kept between the electric field guide window 14 and the dielectric rib 10 within 25 μm. The narrow interval between the electric field guide window 14 and the dielectric rib 10 may cause drawbacks in that the aperture ratio is deteriorated and a stable texture is hard to obtain.
In order to form multi-domains in the related art VA mode LCD device having the multi-domains, it is necessary to provide masks corresponding to the number of the multi-domains to be formed. A corresponding process related with use of each of the masks is performed. For example, to form a multi-domain aligned in four different directions, it is necessary to provide four masks. The provided four masks are respectively used in four processes such that multi-domains each having four different alignment directions can be formed. To this end, the number of the masks increases in proportion to the increase of the number of the domains, causing the manufacturing costs to be increased and the manufacturing process to be complicated.